1. Field of the Invention
The invention relates to the production of high quality optical glasses suitable for incorporation in devices such as lenses and optical transmission lines.
2. Brief Description of the Prior Art
Flame fusion and plasma fusion have been used to form various crystalline and glassy materials using gaseous and particulate feed stocks together with reactive and inert carrier gases (Journal of Applied Physics, 32 (12) p. 2534; Offlegungsschrift No. 2,239,249 Mar. 8, 1973 in German Patent Office). There has been a great deal of recent effort directed to the fabrication of glasses for use as waveguides in the optical and near optical region of the electromagnetic spectrum (Proceedings of the I.E.E.E., 61 (1973) p. 452). Such optical waveguides are required to have a higher index of refraction region surrounded by a lower index of refraction region. The thrust of this work has been the provision of high index and low index glasses exhibiting little absorption or scattering loss at the wavelength desired for optical communication. Factors which effect these losses have been found to be the homogeneity, purity and composition of the glasses used.
Much investigation has been concentrated on fused silica and mixed oxide glasses with a high silica content (Materials Research Bulletin, 8 (1973) p. 469). Many of the mixed glasses investigated, including some of the apparently desirable glasses, include oxides which are significantly more volatile than silica at glass fusion temperatures. This fact presents a problem of composition control during fabrication due to loss of the more volatile constituents.